1. Field of the Invention
The present invention relates to a two-package-mixing discharging device having a discharger for being supplied with two liquids individually fed under pressure and discharging a mixture of the liquids, and a two-package-mixing coating device for individually supplying a base compound and a hardener to respective passages in a dual-tube nozzle in a rotary atomizing head, mixing the base compound and the hardener with each other, and atomizing and discharging the mixture toward an object to be coated.
2. Description of the Related Art
There has been used a two-package-mixing coating (discharging) device for mixing a base compound and a hardener with each other and discharging the mixture to coat an object such as an automotive body or the like. One known two-package-mixing supplying device as such a two-package-mixing coating device is disclosed in Japanese utility model registration publication No. 2506381, for example.
The disclosed two-package-mixing supplying device will be described below with reference to FIG. 7 of the accompanying drawings.
As shown in FIG. 7, a base compound X and a hardener Y are stored in respective reservoir tanks 1a, 1b in which there are disposed ends of respective pressure-feed passages 2a, 2b. The pressure-feed passages 2a, 2b have other ends connected to respective inlet ports of a mixer 3 whose outlet port is connected to a coating gun 4. Gear pumps 5a, 5b are connected respectively in the pressure-feed passages 2a, 2b. The gear pump 5a is connected to an air motor 8 by a speed reducer 6, and the gear motor 5b is connected to the air motor 8 by a speed changer 7.
For setting a mixing ratio for the base compound X and the hardener Y, the speed changer 7 is used to adjust the rotational speed of the gear pump 5b for delivering the hardener Y. Then, the air motor 8 is energized to rotate at a predetermined rotational speed, operating the gear pumps 5a, 5b to supply the base compound X and the hardener Y respectively from the reservoir tanks 1a, 1b to the mixer 3 at a given rate. The base compound X and the hardener Y are mixed with each other by the mixer 3, and the mixture is supplied to the coating gun 4, from which the mixture is applied to an object to be coated (not shown).
Since the main compound X and the hardener Y are supplied from the reservoir tanks 1a, 1b directly to the gear pumps 5a, 5b, the amounts of the main compound X and the hardener Y that are discharged from the gear pumps 5a, 5b tend to vary depending on variations in the pressures which are usually applied to deliver the main compound X and the hardener Y from the reservoir tanks 1a, 1b in the coating site. When the discharged amounts of the main compound X and the hardener Y vary, the mixing ratio for the base compound X and the hardener Y in the mixer 3 also varies, causing properties, such as color, hardness, etc. of the coating on a coated object such as an automotive body to be unstable. Therefore, the properties of the produced coating fail to be uniform.
Another known two-package-mixing coating device is disclosed in Japanese laid-open patent publication No. 2000-126654, for example.
As shown in FIG. 8 of the accompanying drawings, the disclosed two-package-mixing coating device has a coating machine 1c comprising an inner tube 2c, an outer tube 3c disposed coaxially around the inner tube 2c, a rotatable shaft 4c disposed coaxially around the outer tube 3c, a bell cup 5c mounted on the tip end of the shaft 4c, and a lid 6c mounted on the tip end of the bell cup 5c. The inner tube 2c is supplied with a base compound 7c, and the space between the inner tube 2c and the outer tube 3c is supplied with a hardener 8c. 
When the bell cup 5c is rotated at a high speed by an air motor or the like, the base compound 7c supplied to the inner tube 2c and the hardener 8c supplied to the space between the inner tube 2c and the outer tube 3c are mixed into a coating mixture, which is discharged as an atomized mist from a gap 9c between the bell cup 5c and the lid 6c and applied to an object to be coated.
The base compound 7c and the hardener 8c are individually supplied to the bell cup 5c while being isolated from each other by the dual-tube structure. The base compound 7c is introduced from the inner tube 2c into the bell cup 5c in the direction indicated by the arrow H, whereas the hardener 8c is introduced from the space between the inner tube 2c and the outer tube 3c into the bell cup 5c in the direction indicated by the arrow H. Inasmuch as the base compound 7c and the hardener 8c are injected into the bell cup 5c in the same direction, the base compound 7c and the hardener 8c may possibly fail to blend sufficiently with each other even though they are guided along the inner shape of the lid 6c. When the base compound 7c and the hardener 8c do not blend sufficiently with each other, the mixed state of the base compound 7c and the hardener 8c tends to vary, resulting in unstable properties of the produced coating.
The base compound 7c is less liable to change its viscosity upon exposure to air and water. However, the hardener 8c quickly hardens when it contacts air and water. Therefore, the hardener 8c tends to be deposited and hardened on the tip end 2d of the inner tube 2c. If a hardened deposit exists on the tip end 2d of the inner tube 2c, then it causes a change in the discharged amount and direction of the hardener 8c, making properties of the produced coating unstable.
With the disclosed two-package-mixing coating device shown in FIG. 8, because the base compound 7c and the hardener 8c are individually supplied to the bell cup 5c while being isolated from each other by the dual-tube structure, the base compound 7c and the hardener 8c start to be mixed with each other only after they are discharged into the bell cup 5c. However, no attempt is made to design the bell cup 5c to improve the mixed state of the base compound 7c and the hardener 8c, e.g., to specify the distance T from the lid 6c to the tip end of the bell cup 5c. Therefore, the base compound 7c and the hardener 8c are uncontrollably mixed with each other. As a result, the base compound 7c and the hardener 8c may not be mixed sufficiently with each other, causing properties, such as color, hardness, etc. of the produced coating to be unstable.
It is a general object of the present invention to provide a two-package-mixing discharging device which is of a simple structure capable of mixing two liquids individually fed under pressure reliably at a desired mixing ratio.
A major object of the present invention is to provide a two-package-mixing coating device which is of a simple structure capable of mixing a base compound and a hardener reliably in a desired mixed state for effectively improving properties of a produced coating.
A two-package-mixing discharging device according to the present invention has first and second liquid supply passages for supplying first and second liquids fed under pressure from respective first and second liquid supplies to a discharger. The first and second liquid supply passages have first and second gear pumps for delivering the first and second liquids under pressure to the discharger, and liquid pressure control means disposed upstream of the first and second gear pumps.
The liquid pressure control means are capable of controlling the first and second liquids to be supplied to the first and second gear pumps, respectively, under respective predetermined pressures. The first and second gear pumps can thus discharge the first and second liquids at stable rates, so that the first and second liquids can be mixed with each other reliably at a desired mixing ratio.
A two-package-mixing coating device according to the present invention has a dual-tube nozzle disposed in a rotary atomizing head and having an outer tube and an inner tube extending in the outer tube, for individually supplying a base compound and a hardener. The inner tube is arranged to emit a liquid at a liquid emission angle greater than a liquid emission angle for liquid emission from a space between the inner tube and the outer tube.
The base compound and the hardener emitted from the dual-tube nozzle can be aerially mixed with each other and supplied into the rotary atomizing head. The base compound and the hardener are mixed in an effectively improved mixing state. The mixture of the base compound and the hardener which is atomized and discharged from the rotary atomizing head is reliably maintained at a desired mixing ratio, thus producing a high-quality coating on an object to be coated. Since only the liquid emission angles need to be set to desired values, the overall structure of the two-package-mixing coating device is not complex and is economical.
Another two-package-mixing coating device according to the present invention has a dual-tube nozzle disposed in a rotary atomizing head and having an outer tube and an inner tube extending in the outer tube, for individually supplying the base compound and the hardener, and a lid disposed in the rotary atomizing head and defining a coating liquid dispersion opening, the dual-tube nozzle having a tip end which is open in the coating liquid dispersion opening. The rotary atomizing head has a tip end spaced from the lid by a distance L (mm) along an inner surface configuration of the rotary atomizing head, the rotary atomizing head being rotatable at a rotational speed N (rpm), the product Lxc3x97N of the distance L and the rotational speed N being in a range from 400,000 to 900,000.
If the product Lxc3x97N were less than 400,000 when the rotational speed N is in the range from 20,000 rpm to 30,000 rpm, the distance L would be too small, causing the base compound and the hardener to be mixed irregularly and tending to develop color and hardness irregularities in the produced coating on the object. Conversely, if the product Lxc3x97N were greater than 900,000 when the rotational speed N is in the range from 20,000 rpm to 30,000 rpm, the distance L would be too large, causing the base compound and the hardener to be dried and tending to lower the efficiency with which they are deposited on the object and bring about discolorations.
With the rotational speed N and the distance L set in the ranges described above, the mixing state of the base compound and the hardener is effectively improved, and the mixture of the base compound and the hardener is atomized and discharged at a desired mixing ratio to the object to be coated, efficiently producing a high-quality coating on the object. The two-package-mixing coating device is not complex in structure and is economical.